Sunday, November 28, 2010

The last full proposal for a mission to Titan was the Titan Saturn System Mission with a cost of ~$3.4B for the orbiter (FY15 $s) and an additional ~$1B for the balloon and lake lander elements. (Source Titan Saturn System Mission Decadal Survey concept report) At the time of the proposal, reviewers judged that a number of mission elements required further technology development before they would be ready for flight. NASA and ESA tentatively gave the nod to Europa and Ganymede missions subject to the recommendations of the Decadal Survey (Europa) and a competitive selection process (Ganymede).

The TSSM reviewers emphasized that the science was excellent. Further study of Titan would yield significant new advances in planetary research. Recently, several groups of scientists have put forward proposals to study Titan with Discovery (~$425M PI costs) to New Frontiers (~$650M PI costs) (FY10 $s) class missions. These missions address subsets of the TSSM goals in an effort to keep costs down. In this post, I'll continue a series that looks at the trade offs proposed to fit missions to the Saturn system within these budgets. (See New Frontiers to Ganymede and Enceladus and Let's Add an Instrument for previous installments.)

One proposal, the Journey to Enceladus and Titan, would study those two worlds remotely. Little has been published on this proposal. The spacecraft presumably would make multiple flybys of those two moons and possibly orbit one or the other.

Each of these missions attempts to bite off a significant piece of Titan Exploration at less than a quarter the cost of the TSSM mission. TiME and AVIATR been proposed as a Discovery class missions, with the TAE to be proposed as an ESA medium class mission that perhaps has an even tighter budget. (Different budgeting approaches makes it difficult to exactly compare NASA and ESA mission budgets. Both agencies also allow collaboration with other nations, which can add to a mission's funding.) To fit within these budgets, the proposers have reduced mission goals to what appears to be core minimums.

The TSSM balloon platform had goals for studying the structure of Titan's atmosphere, the chemistry of the atmosphere, and remotely studying the surface and subsurface. Both TAE and AVIATR drop the TSSM's mass spectrometer, which would have focused on detailed measurements of atmospheric chemistry. In it's place, both have one or more instruments that would partially replace the science that a mass spectrometer could have performed. However, the organic chemistry of Titan is one of the strongest scientific draws of Titan. This key area of study would have to be fulfilled by other missions.

Instruments proposed for the Titan Aerial Explorer (TAE), the AVIATR plane, and the Titan Saturn System Mission (TSSM) balloon platform. Proposed masses for the TSSM instruments shown for comparison; actual masses of instruments for the TAE and AVIATR missions likely would be different.

In the case of TAE, the proposers might have retained the mass spectrometer by dropping the subsurface radar sounder. (In the TSSM proposal, the mass spectrometer had a mass of 6 kg compared to the radar sounder's 8 kg.) The TAE mission, however, would focus on understanding the methane cycle (analogous to the water cycle on Earth), and the proposers evidently decided that detecting subsurface reservoirs of liquid methane was more central to that goal than atmospheric chemistry. In the case of the AVIATR plane, mass and space constraints would be tight, and the radar sounder would be dropped in addition the mass spectrometer.

The instrument trade offs are less dramatic than the trade off on data rates. The TSSM balloon platform would have returned 300Gb-1.3Tb of data using the orbiter as a relay. The expected data return from the AVIATR mission would be ~2GB. By analogy to previous balloon-only missions to Titan (Titan and Enceladus $1B Mission Feasibility Study), the TAE mission might return a similar amount of data. By forgoing the cost of a data relay orbiter (perhaps an additional $200M based on costs in the Decadal Survey mission concept reports), these missions would forgo significant quantities of data. A simple Saturn orbiter returning to Titan every few weeks likely would not have the relay capabilities of the TSSM orbiter by perhaps an order of magnitude or two, but it would dramatically increase the data return. Since both missions have goals that focus on surface imaging, this is a major reduction in capability compared to what an eventual Flagship mission could do.

Editorial Thoughts: I favor flying one or two Discovery to New Frontiers-class missions to Titan in the next decade (assuming that the Decadal Survey does not resurrect the TSSM mission, which I consider doubtful given its costs and technology readiness issues). These missions would likely be incremental. Eventually, we would need to fly a full Flagship mission, perhaps in the 2020s.

In the next installment, I'll look at the trade offs to enable lower cost Titan lake landers.

Monday, November 22, 2010

I think many of readers of this blog read about a proposed mission and imagine how much the mission might be improved with just another instrument or two or another goal or two. I certainly do.
I learned in my life in a high tech company, though, that "simple" additions often turn out not to be simple and could drive up cost rapidly. For those of us outside of the planetary mission design world, it's hard for us to understand which additions might truly simple additions and which would be unacceptably complex and costly.

The recently published Decadal Survey mission concept studies offer a peak into some of these tradeoffs. Several reports explicitly explore several versions of missions with a variety of goals and instrument costs. In this blog entry, I'll look at examples of the cost tradeoffs for possible missions to Ganymede and Enceladus. The concept studies don't cover all options I would have liked to see discussed. For example, how much would it drive up the costs of an Enceladus orbiter to have an instrument or two to study Titan during several flybys? Or, what would be the design and cost impacts of adding several Europa flybys for a Ganymede orbiter? Still, these reports offer insights that often aren't available to the public. They also were all carried out under the same ground rules and using the same FY15 dollar costs, making comparisons between them reasonable.

The following table list a number of Ganymede and Enceladus mission options. The Ganymede missions differ both in the number of instruments and in the length of time in Ganymede orbit. The Enceladus missions would all orbit that moon for 12 months (except for a multiple flyby mission), but differ in the number of instruments. Several of the Enceladus options were also ranked for relative science value.

Option numbers are from the reports listed at the end of this blog entry. Click on image for a larger version.

The Ganymede mission options range from $1.3B to $1.7B. Looking at the charts in the table, most of the difference in costs appears to be driven by costs associated with building and operating additional instruments rather than the longer time in orbit. This is dramatically shown by adding up the costs to build and test the instruments suites for the Ganymede orbiter. They are $62M, $96M, and $190M for the three options (reserves do not appear to be included in these numbers, so the real costs probably could be higher by ~50%). Additional instruments also require additional operational costs and additional teams of scientists to plan instrument usage and analyze the results. (Instrument costs given do not have reserves included; total mission costs do.)

The Enceladus orbiter missions range from $1.6B to $2.7B. The costs of individual items wasn't detailed in charts, but by examing the graph showing relative cost elements, it appears that this difference again is largely driven by the costs of building and operating different instrument suites.

Costs of individual instruments vary considerably. A magnetometer is only a few million dollars. A mass spectrometer, radio and plasma wave package, or a subsurface radar isseveral tens of millions of dollars.

Even for a specific instrument type, costs can vary considerably. The simpler Ganymede mass spectrometer apparently would cost ~$25M to build while the more sophisticated Enceladus mass spectrometer would cost ~$57M. (Note: For some items, I'm making educated guesses to determine which instrument costs in the reports go with which instruments.)

Neither the Ganymede nor Enceladus mission reports spell out the cost of a narrow angle camera (NAC), which would be useful for exploring their target worlds and really useful for observing the rest of the Jupiter or Saturn systems. However, it appears that instrument #10 in the Ganymede report at ~$13M is the NAC and the Io observer NAC is listed at ~$17M. These are simple cameras compared to those proposed for the Titan and Europa flagship missions that proposed NACs costing ~$54M and ~$43M respectively. A lot of capability is given up to keep the costs of these Decadal Survey concept missions below the Flagship mission costs.

Editorial Thoughts: My favorite instrument to add to an Enceladus mission would be a 2-micron imager that would use a spectral window in the atmosphere for high resolution imaging of Titan. The specific costs of that instrument wasn't spelled out in the reports. However, assuming that its cost might be similar to that of a NAC (similar optical and mechanical design but a different sensor, I think), then the final cost to the mission might be $35-40M with design, fabrication, testing, operation, analysis.

I would hate to see a mission go to Enceladus and not carry this instrument. However, it might be that adding this instrument would bust the budget and jeopardize approval of the mission. In my experience, engineers are very creative at exploring all the options. Then they become hard nosed about what has to be left out to fit within the financial, manpower, expertise, and weight restrictions. If this instrument can be flown within those restrictions, I expect that it will be. In the meantime, I can imagine what such a mission might do.

Friday, November 19, 2010

Lately, spam comments have out numbered real comments. To try to control this, I have enabled moderation on comments. All legitimate comments will be posted. But if you want to sell something (especially viagra) or want a link to a blog with no relevance to space exploration or science, your comment won't be posted.

Jonathan Lunine at the University of Arizona has just posted his intent to develop a proposal for a Titan Aerial Explorer. From his announcement, "The mission to be proposed includes a balloon with the capability for ground-penetrating radar, radio science and multi-spectral imaging and spectroscopy, aerosol analyses, and possibly other instruments. The goal is to explore the processes that are at work on the surface on and near-surface of Titan with sufficient resolution and wavelength capability to quantify Titan’s methane hydrologic cycle." The proposal would be submitted for the European Space Agency's next Medium class science mission for launch around 2022.

Editorial Thoughts: I would like to see one or more Titan in-situ missions fly in the 2020's. Titan's thick atmosphere and low gravity makes it an easy world (once you spend many years flying there) to land on, float above, or fly around. Lunine's mission potentially would face several challenges such as power (ESA currently does not have plutonium power sources, which as I understand it would be necessary both for power and to heat the gases for the balloon) and bringing the balloon technology up to flight readiness (the Titan Flagship mission's balloon reportedly was judged to require further technology development before flight). However, Dr. Lunine has a solid resume, so he must have ideas on how to address these problems.

Wednesday, November 17, 2010

In my previous post, I listed missions to explore the diversity of icy ocean moons such as Europa, Ganymede, Titan, and Enceladus as my third and fourth picks for my most compelling missions. This post begins a series that looks at approximately New Frontiers-class missions to these worlds based on mission concepts examined by the Decadal Survey.

From my examination of the mission concept studies from the Decadal Survey, it appears that there were two classes of missions examined. The first were flagship class missions costing over ~$2B. These were the three missions composing a Mars sample return, the Europa Jupiter System Mission, and the Titan Saturn System Mission. (There were also some Flagship-scale options in other reports.) In addition, the Survey commissioned a number of concept studies for missions that might fit within the New Frontiers class of missions (~$650M for principle investigator costs; ~$1.2B for NASA's fully burdened costs). All costs in the studies were for FY15 costs, when the burdened costs of a New Frontiers mission (assuming 3% inflation per year) would be ~$750M for the PI costs and ~$1.4B for the fully burdened costs*. (The Survey reportedly will recommend specific Flagship and New Frontiers-class missions; it will not recommend specific missions for the lower cost Discovery missions.)

Several New Frontiers class missions were studied for the icy moons of Jupiter and Saturn:

Several incremental flavors of a Ganymede orbiter that would also conduct several flybys of Callisto

A number of variations of Enceladus missions that included flybys, orbiters, landers, and flyby sample returns along with flybys of other moons of Saturn

Four variations of probes to float on or descend into one of the polar lakes of Titan

Option numbers are taken from the reports listed below. Missions in the Enceladus Flyby & Sample Return Concept Studies report were ranked by the relative value of the science they would be expected to return. Click on table for a larger image.

In this post, I'll begin looking at the orbiters of Ganymede and Enceladus. Unfortunately, the concepts studies for Enceladus landers and flyby sample returns determined that these missions are premature. For landers, we don't understand the nature of the surface (fluffy snow or rock hard ice? gentle plains or steep slopes?) and for sample returns there are uncertainties associated with the design of the sampling mechanism (a derivative of the Stardust aerogel collector) requiring "a significant technology development" as would issues of ensuring sterilization of the return probe for planetary protection. The studies concluded that for Enceladus, an orbiter represents the most attractive target for the next mission (after Cassini) to this moon.

In several ways, a mission to Ganymede and Enceladus have similar requirements. Both must travel to and operate in the outer solar system. Both would study icy ocean worlds, and hence their list of desired instruments are similar. However, there are also important differences. A Ganymede orbiter is close enough to the sun that solar panels could be used. An Enceladus orbiter is far enough from the sun that the safe bet is on plutonium-powered spacecraft (ASRG's). An Enceladus orbiter would study a tiny moon so close to its dominant planet that a polar orbit would be unstable. Instead, the southern polar geysers and terrain would have to be studied during a series of flybys prior to orbit insertion. The final orbit could not exceed 60 degrees latitude to ensure a stable orbit.

While missions with costs in the $1.3-1.6B range are possible for both moons, the capabilities of the instruments suites would differ considerably. For $1.6B, the Ganymede orbiter would carry the full suite of desired instruments. For the same cost, the Enceladus orbiter would have to forgo desirable instruments such as a narrow angle camera, an imaging spectrometer to study the composition of surface materials, and an ice penetrating radar to directly detect the presence of a subsurface ocean. These instruments could be added to an Enceladus orbiter, but only by increasing costs to almost twice that of a New Frontiers-class mission.

Either mission, however, would substantially expand on the knowledge of their target moons. A Ganymede orbiter has been a priority mission for NASA for several years and is currently in contention as an ESA mission. The discovery of active geysers at Enceladus have made it a priority since it provides our only near term option to directly sample the composition of an icy moon's ocean in the next two decades. In lieu of a Flagship mission to study the moons of either Jupiter or Saturn, these seem to be worthy missions.

In my next post, I'll look at the impact of instrument costs on options for exploring these two moons.

*Note: The budgets for New Frontiers missions are something of a mystery to me. The PI budget is stated in the Announcements of Opportunity, and the fully burdened cost can be derived from NASA's New Frontiers budget line and include some obvious big ticket items like launchers. The Decadal Survey studies seem to be giving cost estimates somewhere in between these two numbers. As near as I can determine, the budget for a New Frontiers mission using the items included for FY15 would be between $1.0B and $1.1B. Source reports:

Friday, November 12, 2010

This blog entry continues the series to pick the 5 missions that I personally find most compelling for the next decade. I'm under no illusion that I will persuade anyone (especially anyone who influences government spending). However, I find a well argued (and I hope these will be) argument to help me form my own opinions. Please provide your opinions, too, in the comments. You can find the earlier installments of this series at these links: Mars Caching Rover and Venus Climate Flagship.

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Concept for a Ganymede Orbiter

Over the last fifteen years, we've come to learn that icy worlds with internal oceans appear to be common in the solar system. At scientific conferences, sessions are devoted both to individual worlds such as Enceladus and Titan where we have newly arriving data and to comparing these worlds with the moons of Jupiter, Triton, and Pluto . The AGU conference this December will have sessions on "The Potential for Water-Organics Interactions on Titan," "Eyes on Enceladus," "The Amazing Nature, Origin, and Evolution of Outer Planet Satellites", and "Icy Ocean Worlds" to name just a few. (As a side note, I appreciate the AGU scheduling these sessions this year so that they largely don't overlap with the sessions on my field of study.) For the first two picks in my list of compelling missions, I chose missions that would advance the comparison of terrestrial worlds with atmospheres. For my third and fourth picks, I my choice is for two missions to advance the comparison of icy ocean moons.

The Decadal Survey's list of missions it considered (it's made its selections, but we won't learn of them until next March) is rich with missions to pick from. There are the Flagship missions to Europa and the Jovian system and to Titan and Enceladus at the high end with price tags of $2.7B and $3.2B, respectively. (All costs are from the just released mission studies and were stated in the reports in FY15 dollars. The two Flagship missions have been studied in depth, and their costs probably have greater fidelity than the other costs listed, which represent early assessment costs developed as part of the mission concept studies.) At the low end, there is an option for an Enceladus multiple flyby mission for $1.4B. In between are Enceladus orbiters ($1.6B - $2.4B), a Ganymede orbiter ($1.35B - $1.7B), and Titan lake landers ($1.3B - $1.5B). My choices for the third and fourth missions on my list would be one to explore the icy moons of Jupiter and one to explore Titan and Enceladus.

Ideally, NASA would fly the Europa Jupiter System Flagship mission along with a capable Enceladus orbiter (that would also do multiple Titan flybys) and a Titan lake lander. However, this combination would cost almost $6B. Combine that with a $3-4B investment in Mars missions (which I predict will be the Decadal Survey's top priority) and a couple of Discovery missions, and that's pretty much the entire budget for missions next decade. I also think that the Flagship missions may face have a couple of programmatic challenges. First, NASA's last two choices for Flagship-scale missions, the Mars Science Laboratory and the James Webb Space Telescope, both experienced large cost overruns. The latter mission is facing another large cost overrun, and that may make the Survey and NASA skittish about recommending another large mission. The second challenge is that NASA apparently does not have the plutonium 238 on hand to fly a Flagship mission. They apparently will receive sufficient Pu-238 if Russia resumes sales or if Congress funds new production. Will NASA want to bet a large chunk of its planetary mission budget on these two ifs?

I hope that these issues can be overcome. If they can't, my next three posts will look at the lower cost mission alternatives presented in the Decadal Survey's studies for studying Jupiter and Saturn's icy ocean worlds.

Tuesday, November 9, 2010

As part of its analysis, the Decadal Survey commissioned 25 mission studies to define potential missions it would select its final list from. The full list of mission studies, plus three technology studies to enable missions in the 2020s and beyond, have been posted (http://sites.nationalacademies.org/SSB/SSB_059331). As one poster at Unmanned Spaceflight put it, this is a candy store for those interested in future planetary missions.

In future entries, I'll be summarizing the reports (a typical length is around 30 pages) and where appropriate comparing them to each other and to past missions and other mission concepts. Generally, each report will get its own entry, but in the case of similar mission types, I'll compare the mission concepts in a single entry. I'll also combine the summaries with my continued list of the five missions that I find most compelling for the coming decade.

To kick off the process, I'll post a table comparing the missions for cost and mission flight times (be sure to read the notes on the table for important caveats). In going through this list, I was happy to see that a large number of missions are reasonably close to the fully burdened New Frontiers mission cost of ~$1,350M inflated at 3% per year for Fiscal Year 2015 costs. Another group of missions could probably fly at a New Frontiers mission and a half budget. Assuming that the Max-C rover, the Mars Trace Gas Orbiter, and three Discovery missions fly in the next decade, this would allow two to four of the sub-$2B missions on this list to fly.

Click on the list for a larger version.

Notes on the table:

A number of the reports analyze several options for a mission target. In this case, I picked either the lowest cost or a typical cost and did the same with the mission timeline.

The mission dates can be somewhat arbitrary. For many missions, launch windows occur every year to every few years. For the purposes of the studies, a given time frame was chosen. Use the dates to get a feeling for how long the flight to the target would take and how long science would be gathered at the target. For missions that would involve multiple targets or that require entry into orbit around Jupiter or Saturn, the arrival date is the date at the first target or orbit insertion around the major planet.

The cost estimates were prepared by the mission assessment teams. These are not the rigorous cost estimates that will be prepared by an independent team for a subset of these missions that the Survey considered most likely to be recommended. The costs, therefore, should be considered approximations. A difference of a couple of hundred million dollars may not be significant, while a difference of a billion dollars almost certainly is. In addition, early cost estimates are often low, and many of these estimates may also be low. Where the various mission options came with widely different costs, I showed the range of estimates.

The next blog entry will describe the two mission concepts that together would be for me be the third most compelling mission for the coming decade.

Wednesday, November 3, 2010

Anyone not living in a cave has heard that the elections in the United States have resulted in a more conservative Congress promising to reduce the federal deficit. Budget tightening in the United States is hardly unique. As the Wall Street Journal reported last summer, ESA may be facing its own budget problems, or at the least not growing its programs as fast as some would hope. (Subsequent news from Europe seems to suggest no ESA budget cuts in the short term.)

This blog is purposefully not political. If you want to argue politics, there are many good blogs and discussion boards for that. I will not discuss whether or not I think the federal budget should be cut. Rather, I want to explore the implications of some ideas that have been put out by newly ascendant Republican leadership.

As I have done for previous analyses of budgets for future planetary missions, I have added up the budget amounts for future mission development and current mission operations. (This leaves out funds for scientific research and R&D.) I have then multiplied the current year budget by ten as an estimate of funding available for the next decade. This assumes that future budget increases match the inflation rate, and that funding for operation of missions that have yet to launch will be similar to funding for missions currently in flight. So, this is a fairly simplistic analysis that makes use of easily obtained public budget documents.

Here are some key budget figures:

FY08 ~$949M (approved) or ~$9.5 over a decade
FY10 ~$1.1B (approved) or ~$11.0B over a decade
FY11 ~1.16 (proposed) or ~$11.6B over a decade

The proposed FY11 budget has not been approved. The politics get murky at this point, but based on precedence, NASA's planetary program is likely to be funded in FY11 (Oct. 2010 to Sept. 2011) at about the FY10 rate. The difference over a decade would almost fund an additional Discovery mission at the fully burdened rate (or ~$800M which includes costs above the $450M available to the principle investigator).

If the budget is reduced to FY08 levels, then NASA's looses ~$1.5B over a decade compared to the FY10 budget level, or a bit more than the burdened cost of a New Frontiers mission.

If NASA's budget for future missions was frozen for a decade, NASA would lose about the equivalent funding of a New Frontiers program whether the initial level is at FY08 or FY10 budget levels. If the starting budget was the FY08 level and then frozen, then the result would be the loss of funding equivalent to approximately two New Frontiers missions compared to the FY10 budget level increased for inflation.

Editorial thoughts: In one important sense, this analysis is extremely simplistic. NASA has two major programs, the manned program and the unmanned science program of which planetary exploration is a part. (And even this is simplistic since it leaves out aeronautical research.) NASA's manned spaceflight program is at a crossroads. Meeting either the ambitious return to the moon goals of President Bush or the go to Mars via near Earth asteroids goals of President Obama requires high levels of funding. It is my observation that the manned side of NASA gets more political attention than the science side. It is quite possible that any budget cuts would not be applied equally to the two sides, and the net impact on future planetary missions may be greater than the quick analysis above suggests.

Planetary exploration is discretionary spending. Nations budget for it after they fund what they see as the core needs of their people. If the political process in the United States or elsewhere determines that spending levels must be reduced, I would not argue for special dispensation for planetary exploration. Rather, I hope that the program that will be recommended by the Decadal Survey will be flexible enough to remain viable if spending cuts do occur.

About Me

You can contact me at futureplanets1@gmail.com with any questions or comments.
I have followed planetary exploration since I opened my newspaper in 1976 and saw the first photo from the surface of Mars. The challenges of conceiving and designing planetary missions has always fascinated me. I don't have any formal tie to NASA or planetary exploration (although I use data from NASA's Earth science missions in my professional work as an ecologist).
Corrections and additions always welcome.